Hello, everyone!
I run the code below and it worked perfectly until I changed from 'filter(x, is.na(dep_time))' to 'filter(x, !is.na(dep_time))'. I lost all my observations in environment. However, when cleaned the environment and run 'filter(x, !is.na(dep_time))', it worked again.
library(dplyr)
library(nycflights13)
fl = flights
fl = fl %>% filter(is.na(dep_time))
dim(fl)
Why does it happen?